Solution of zein in solvents acidified with inorganic acids



Patented a. 13, 1942 somrrou or zam IN sorvsn'rs seminar; wrrrr monosmcscrn film E. Coleman, Meriden, com, sinner, by

corporation of New Yo No Drawing. Application Serial No. 219,827

assignments, torkilime, Incorporated, a

14 Claims. (c1. roe-s) This invention relates to liquid coatingcompositions and solutions made from zein or other prolamins; and moreparticularly to substantially non-aqueous solutions of zein in acidifiedsolvent mixtures and to the methods of preparing same. The solutions orcoating compositions prepared in accordance with my invention do notseparate on standing, have a definitely delayed or retarded tendency togel and, in some instances, are non-gelling over periods of time in theorder or 3 to 6 months and even more.

In the following description of my invention I refer to the preparationof non-separating, substantially non-gelling solutions or coatingcompositions of zein derived from corn, but it is, of course, to beunderstood that my invention is also applicable to the preparation ofsolutions or coating compositions made from other prolamins such as, forexample, gliadin' from wheat, hordein from barley, kafirin from kafirand the prolamins from other cereal grains. The abovementioned prolaminsare at present ordinarily derived by extractionof the gluten of corn orother grains with an aqueous alcohol solution in which the added watervaries generally from about 8% to about 40% of the solvent mixture, theextract so produced being dried, forming a dried prolamin extract whichmay be completely dry. or in commercial form ordinarily contains a smallpercentage of moisture. Such prolamin extract, such as zein extractedirom corn, may be used. in accordance with myinvention, although zein orother prolamin obtained in any other suitable manner may also be used.

In accordance with the prior art methods of making zein solutions orcoating compositions wherein zein is dissolved in a solvent such asmethanol, isopropanol, butanol, and other lowmolecular weight alcohols,glycol ethers and the like containing relatively large quantities ofwater in the order of over 5% and up to about 30% and higher, thesolutions or coating compositions formed are not suitable for use overpractical periods of time because-of a tendency to thicken and in manycases to gel. The presonce of these relatively large percentages ofvwater and other factors such as concentration of zein in the solutionsor coating compositions, and'the presence of solvents such asthose'mentioned above, particularly methanol, contribute to thethickening or gelling-of the solutions or coating compositions onstanding.

In my prior copending application, Serial No.

158,209, filed August 9, 1937, Idescribe and claim methods or preparingsubstantially nonaqueous solutions ot zein in alcohol containing 5% andless of added water wherein the zein varies in weight from aboutone-third to about one-fourth of the solution. These solutions arestable as regards separation in the cold, that is, at temperatures under80 F. andat temperatures of F. and somewhat lower. In my prior co lending application Serial No. 158,215, iiled 'Augustm'i'firowpatektedfimniber 26, 1939,

other solutions which also are stable as regards separation at thesetemperatures.

In particular, in my prior application Serial No. 158,215, now patentedDecember 26,1939, No. 2,185,124, I described solutions and liquidcoating compositions containing prolamins and particularly zein whichare anhydrous or substantially anhydrous and which, in concentrations inwhich the proportion of solvent to zein is from 2:1 upward,'and moreparticularly from 4 to 5:1, are stable in the cold in that they do notseparate or form and deposit a separate phase or layer containinglargely zein with a supernatant layer of liquid consisting largely ofsolvent. The production ofsuch stable solutions is important inconnection with the utilization of zein and similar prolamins in theproduction of coating compositions and the like,.since they enable thezein to be put in a homogeneous and usable form either for direct use orfor compounding with other materials, solvents, non-solvents, coatingand film-forming materials and the like.

It has been found, however, that the zein solutions of the prior art andeven some of the stable character hereinbefore referred to are limitedin their application and use because of a tendency, which frequentlyappears, to increase in viscosity; that is, to thicken or to becomeheavier in body; and in many cases to gel. Such tendencies to increasein viscosity, or to gel, while not preventing the utilization of thecompositions immediately or within short periods after preparation, doimpose serious limitations on their wide-spread commercial applicationand utilization, since the materials must remain stable and reasonablyconstant intheir characteristics during the periods necessary rortransportation and distribution either in bulk or in packages, and topermit of reasonable periodsof storage.

In accordance with the present invention, I a have developed solutionscontaining prolamins which is ordinarily a preliminary of gelling, are

No. 2,185,124, I claim these solut ons"asweil as I delayed or retardedand in many cases completely prevented so as to greatly increase thefield of applicability and to permit wider distribution and conventionalhandling of the manufactured products, without material change incharacteristics or solidification by gelling over such reasonableperiods oftime as are involved in such handling and distribution of thematerials.

I am of the opinion that the phenomenon of gelling of such solutions andcompositions and their increase in body or viscosity as a whole areprobably related to the phenomenon of separation, since where separationtakes place in many cases the separated phase containing largeproportions of zein is itself a gel in character: and since also in manycases compositions containing zein which tend to separate when theproportion of solvent to zein is as high as 3:1 and higher will gel as awhole with lower proportions of solvent or higher concentrations ofzein; and also since many solutions which ,are stable and. do notseparate when the proportion of solvent to zein is from 2 to 2.5:1 orhigher will form gels as a gelling thereof to an extent not heretoforeattainable and in many instances, prevents gelling overconsiderableperiods of time, for example, in

' the order of about three to six months and even whole if they containhigher proportions of zein.

However, in the consideration of the tendency to gel and to increase inviscosity or body as referred to in the present application I havereference to' the tendency tsolutiensw gel 'asa --l! i91e.or..-teincrease' in viscosity through their entire mass, in cases inwhich the proportions of solvent to zein are in the order of 2 to :1 andhigher, up to 9 or 10:1, which are the solutions and. compositions of aconcentration which is most important from the standpoint of theproduction of films, coatings and the like and which range ofconcentrations is more particularly referred to in my prior co-pendingapplications. relating to the production of stable solutions. It is tobe'appreciated that solutions or compositions which are stable and inwhich the tendencies to gel and to increase in viscosity are adequatelyretarded or prevented within this range of concentrations may, withhigher concentrations of zein, be more likely to form gels; but in anycase the-compositionsprepared in accordance with the present inventionwill have a less tendency to form gels or to increase in viscosity thanthe solutions hitherto known.

In accordance with my present invention, 1

tially non-aqueous denatured alcohol or other zein solvent.

The solvent mixtures used in accordance with the present invention arecharacterized by the presence of both an alcoholic and an acidcomponent. The liquid coating compositions prepared in accordance withthe present invention may be anhydrous or substantially non-aqueous, asdesired. In instances where water is added to such coating compositionsthe amount of added .water should not, in general, materially exceed 5%and should preferably be less than 5%. Accordingly,my preferred coatingcompositions are, for all practical purposes, substantially non-aqueous.The presence of theacid component in the coating compositions definitelydelays or retards the alcohol to aid solution.

where one or more of the low-molecular weight alcohols or denaturedalcohols of the character set forth above are used in the solventmixture, but also where other zein'solvents such as glycol ethers, areused. The presence of an acid component in a solvent mixture comprisingsuch zein solvents as, for example, the anhydrous or substantiallynon-aqueous glycols, diacetone alcohol, benzyl alcohol, furfurylalcohol, cyclohexanol and like alcohols, and the alcohol ether,diethylene glycol monomethyl ether not only enhances their ability todelay or retard gelling but also appears to reduce the viscosity of theresulting. solutions.

The acid component used in conjunction with a zein solvent to formcoating compositions in accordance with the present invention ispreferably an inorganic acid such as hydrochloric, phosphoric, boric andthe like. Other inorganic acids such as sulphuric, nitric and the likemay also be used but these are not preferred. If desired, part of theinorganic acid may be replaced by an inorganic acid salt such as, forexample, magnesium sulphate, aluminum chloride, sodium sulphate, leadacetate, aluminum phosphate, aluminum sulphate and like acid salts. Theacid component may be used in powder, crystal or liquid form depending,of course, on the form which is commercially available. If the alcoholis incapable of readily dissolving the desired amount of the acidcomponent, small amounts of water, within the limits stated, may beadded to In the instances where the alcohol already contains water,solution of the desired amounts of acid component in the alcohol aflordsno particular problem.

The quantity of acid component which may be used in admixture with thealcohol in accordance with the present invention may vary widely, butsumcient should be used to render the alcohol definitely acid and at thesame time not so large an amount should be used as will affect thecharacter of the zein. 'I have obtained satisfactory results with theuse of an inorganic acid in amounts varying from about 1% to 2% and upto 20% and even higher of the solvent mixture although for most purposessatisfactory results have been obtained with the use of acids inproportion varying from 3% to 8%. In general, the quantity of acidcomponent'required in the solvent mixture to prevent separation and toretard and prevent gelling varies with the concentration of zein in thesolvent; with high concentrations of zein,

larger amounts of the acid component are required and with lowconcentrations of zein, smaller amounts of the acid component arerequired.

for example, a kettle, usually with some stirring and with theapplication of heat in the order of about 110 to 150 F. A stablesolution of the zein in the solvent mixture is obtained generally inabout 3 to minutes, and in most instances satisfactory stable solutionsare obtained in about 3 to 10 minutes with the utilization of heat inthe order of about 120 to 135 F.

The present invention is illustrated by the following examples ofcoating compositions embody-' ing my invention and of the methods ofpreparing the same; however, my invention is not to be construed aslimited thereto since other suitable compositions in other suitableproportions are intended to be included within the scope of my claims.In the examples, the term parts" indicates parts by weight. Also in theexamples, when I refer to anhydrous denatured alcohol I have referenceto the commercial anhydrous denatured alcohol of the following formula:

Per cent Anhydrous ethyl alcohol approximately.. 89.3 Anhydrous methylalcohol do 4.4 Ethyl acetate do 6.3

' When I refer to hydrated anhydrous denatured alcohol I have referenceto an alcohol solvent mixture containing 95.6% of the above anhydrousdenatured alcohol and 4.4% of water.

Example 1 10 parts of zein are mixed with 47.5 parts of anhydrousdenatured alcohol and 2.5 parts of C. P. hydrochloric acid in a suitablevessel and the'mixture is heated to about 120 F. for about 3 to 5minutes to form a clear, stable solution of zein. The solution formeddoes not separate, settle or gel on standing at room temperature or evenwhen cooled to about to F.

Example 2 Y 10 parts of zein are-mixed with 47.5 parts of hydratedanhydrous denatured alcohol and 2.5

parts of phosphoric acid (U. S. P. in a suitable vessel and heated toabout to F. for about 5 to 7 minutes to effect solution. The solution onstanding at room temperature in the order of about 60 to 70 F. shows notendency to separate, settle or gel.

Example 10 parts of zein are mixed with 38 parts of hydrated. anhydrousdenatured alcohol and 2 parts of powdered boric acid in a suitablevessel and heated to about to F. to effect solution. The solution onstanding shows no tendency to separate or settle. On coolingthe solutionto below 50 3'. no separation or settling takes place Example 4 hardlight, pale, straw color not heretofore attainable 75 described in aeinsolutions. These solutioim have a definitely delayed or retardedtendency towards selling and in some instances do not gel even overconsiderable periods of time, for example, in the order of about 3 to 8months and even higher. Moreover,

these solutions are stable in so far as separation small amount of addedwater and are, therefore,

substantially non-aqueous.

The coating compositions prepared in accord-1 ance with the presentinvention have the unusual property, particularly when heated, of beingable to give up their solvent or solvents readily when. applied to anysurface and they readily form tough, fiexibile, non-tacky, hard andgenerally transparent films. The films are very strong and have unusualadhesive properties. They are not readily inflammable as are films ofsuch substances as nitrocellulose, pyroxylin and the like. The mm areoil-resistant and provide an excellent printing surface for any type ofink. With the aid of these coating compositions, film-forming propertiescan be built up to produce a film ingcompositions containing added wateras in ..the prior art.

'bodylngmyinventionandhenceoftheultimateiilmscanbealteredatwillandasdesiredbythe copal,phenol-aldehyde, Dhthalic anhydrid, vinyl and ening liquid coatingcompositions of the type;

and claimed in my prior copending apof greater toughness, flexibility,hardness and gloss than is capable of being formed from coat- Thecoating compositions embodying my invention may be applied to anysurface, including surfaces coated, for example, with varnish, lacquer,rubber or .cellulose derivatives and form hard, adherent films thereon.They may be used format- 118, sizing, impregnating and waterproofingvarious materials such as paper, textiles, wood, porous stone, wood pulpand the like. When coated on paper, Cellophane, glass and the like, anonblushing film is formed almost immediately which possesses the filmcharacteristics set forth'above. Since these coating compositions havedecided adhesive properties before setting they may be used for unitingor laminating Paper, cloth, wood, ighlaslsikeailk, Cellophane, metalsand metal foils and The characteristics of the substantially nonaqueousrein solutions or coating compositions eminelulion in the coatingcompositions of diluents, modiflemplasticisersandthelikeassetforth in myabove-identified copending application Serial No. 153,215. I'hecharacterlstics,' such as spread and flow of the coating compositions,may also be modified by the such as, for example; ol'eic, linseed, hempseed. laurlc and like fatty acids, by the inclusion of blown or bodieddrying oils such as blown Chinawood oil or other oxidizing oils, and bythe inclusion of cetyl, lauryl, myristyl and like fatty alcohols having8 or more carbon atoms in the chain If desired, compatible natural andsynthetic resins such as, for example, rosin, sandarac,

urea-aldehyde, glycerinlike resins, or heataddition of a fatty acid,

positions.

piication Serial No. 177.302, flied November 30, 1937, now patentedDecember 26, 1939, No.

2,185,121, or compatible cellulose derivatives such I as, for example,highand low viscosity nitrocellulose, cellulose acetate, ethyl celluloseand like cellulose derivatives may be incorporated with the liquidcoating compositions in varying proportions to meet any desired need.

If desired, suitable tillers such as, for example,

'those set forth in my application Serial No.

158,215 new patented December 28, 1939, No. 2,185,124, can beincorporated in the coating com- I claim: I

1. A coating composition comprising asolution of a prolamin in a solventmixture characterized by the presence of an alcohol and an inorganicacid, said solvent for thezein containing not in excess of of water,said composition containingnot in excess of about 5% of added water andbeing stable against separation of the prolamin at temperatures of 70 F.and being substantially non-gelling.

2. A substantially non-aqueous coating composition comprising a solutionof zein in an inorganic acidified alcohol solvent containing not inexcess or 5% of water, said composition containing not in excess ofabout 5% of added water and being stable against separation 01' the zein7. A coating composition comprising a solution of zein in a solventmixture containing an alcohol, an inorganic acid, and an inorganic acidsalt, said solvent for the zein containing not in excess of 5% 0! water,said composition containing not in excess of about 5% oi added water andbeing stable against separation of the zein at temperatures of 70 F. andbeing substantially non-gelling.

8. A substantially non-aqueous coating composition comprising a solutionof zein in a solvent mixture containing a denatured alcohol and aninorganic acid, said solvent'ior the zein containing not in excess oi.5% of water, said composition containing not in excess of about 5% ofadded water and being stable against separation of the zein attemperatures oi! 70 F. and being substantially non-gelling.

9. A coating composition comprising a solution 0t zein in a solventmixture containing an alcohol and hydrochloric acid, said solvent forthe zein containing not in excess of 5% of water, said compositioncontaining not in excess of about 5% of added water and being stableagainst taining not in excess 01.5% of water, said compositioncontaining not in excess of about 5% of added water and being stableagainst separation of the zein at temperatures of 70 F. and beingsubstantially non-gelling.

4. A substantially non-aqueous coating composition comprising a solutionof zein in a solvent mixture containing a substantially neutral, hydroxyorganic zein solvent and an inorganic acid, said solvent for the zeincontaining not in excess of 5% of water, said composition containing notin excess of about 5% of added water and being stable against separationof the zein at temperatures of 70 F. and being substantiallynon-gelling.

5, A coating composition comprising a solution of zein in a solventmixture containing an alco hol and an' inorganic acid, said solven't'forthe zein containing not in excess of 5% of water. said compositioncontaining not in excess of about 5% of added water and being stableagainst separation of the zein at temperatures of 70 F. andbeingsubstantially non-gelling.

6. A coating composition comprising a solution of zein in a solventmixture containing a substantially neutral, hydroxy organic zein solventand --hydrochloric acid, said solvent for the zein con-- taining not inexcess 0! 5% of water, said composition containing not in excess ofabout 5% of added water and being stable against separation separationof the zein at temperatures 01' 70 F. and being substantiallynon-gelling.

10. A coating'composition comprising a solution of zein in a solventmixture containing an alcohol and phosphoric acid, said solvent for thezein containing not in excess of 5% or water, said compositioncontaining not in excess 0! about 5% 01' added water and being stableagainst separation oi. the zein at temperatures of 70 F. and beingsubstantially non-gelling.

11. A coating composition comprising a solution of zein in a solventmixture containing an alcohol and boric acid, said solvent for the zeincontainingnot in excess of 5% of water, said composition containing notin excess of about 5% of added water and being: stable againstseparation of the zein at temperatures of 70 F. and being substantiallynon-gelling.

12. A substantially non-aqueous coating composition having a solution ofzein in a solvent mixture containing a substantially neutral, hydroxyorganic zein solvent and phosphoric acid, said solvent for the zeincontaining not in excess of 5% of water, said composition containing notin excess 01 about 5% of added water and being stable against separationoi! the zein at temperatures of 70 F. and being substantially nonof thezein at temperatures of F. and being substantially non-gelling.

gelling.

13..A coating composition comprising a solution of zein in an acidifiedethyl alcohol solvent containing .not in excess of 5% of water. saidcomposition containing not in excess of about 5% of added water andbeing stable against separation of the zein at temperatures of 70 F. and

